Amazon has rapidly built up an infrastructure around Twin Cities — and around the U.S.

Just four years ago, Amazon had no physical presence in Minnesota.

Then came an 855,000-square-foot fulfillment center in Shakopee, along with a smaller nearby sorting center. A delivery station in Eagan. A Prime Now hub in an industrial park in Minneapolis.

And, most recently, a new and expanding tech office in the trendy North Loop.

"It's growing at an incredibly fast rate based on an incredibly large amount of volume it's doing," said Thomas Paulson, a Minneapolis investment analyst who has followed Amazon for more than a decade.

While the Twin Cities did not make the list of finalists for Amazon's highly sought-after second headquarters, with up to 50,000 high-paying corporate jobs, the company's local operations are growing quickly and now employ more than 2,300 people.

Amazon continues to rapidly expand its infrastructure in major metro areas around the country as it works to get closer to where consumers live and to more quickly and cheaply dispatch packages to them.

The company had 563,100 workers at last count and is adding more at upward of 60 percent a year. It has surpassed big employers like Minneapolis-based Target Corp., which has 345,000 people, and Paulson believes Amazon could have more than a million people in its ranks by 2020.

"It's mind-blowing," he said. "I don't know how their HR is doing it."

Many of those workers are in one of Amazon's 175 fulfillment centers worldwide, such as the one in Shakopee. The facility, which opened in July 2016, is in operation around the clock with about 2,000 workers who work 10-hour shifts four days a week.

Dubbed "MSP1" — the company names its warehouses using the code for the nearest airport — the operation is one of only 25 in Amazon's network that use a cutting-edge robotics platform.

Behind a chain-link fence, thousands of circular orange robots that resemble Roomba vacuums have millions of square feet to cruise over four floors, scurrying like mice shuffling among stacks in a library.

The aisles are full of pods — nine-level shelving units stocked with coffee filters, phone chargers, and hundreds of thousands of other products Amazon customers might purchase. The facility can send packages anywhere around the United States, but mostly ships to addresses around the Upper Midwest.

When an order comes in, a robot is directed to the closest pod that has that item, lifts the whole unit slightly off the ground, and then transports it, moving about 3 miles per hour, to one of dozens of picking stations.

"One of the cool things here is that just like Minneapolis, which has freeways and highways, we have high trafficked kind of roadways," said John Russell, director of operations.

At the picking stations, workers like Evan Collins glance up at a screen that shows a picture and description of the item and which shelf to find it on. He grabs it, scans it to verify it's the right item, and places it into one of several yellow totes lined up to his right.

He hustles back and forth from pod to tote, pod to tote.

"It's a good workout," said the 26-year-old Bloomington resident, adding that he's lost 40 pounds since he started the job nine months ago.

He had just moved back home after living abroad and his insurance was about to expire when he saw an ad on TV that the fulfillment center was hiring with starting wages around $15 an hour and benefits. Two days later, he was hired.

He said workers are encouraged to go as fast as they can while being safe and doing it right. The average picker handles about 400 items an hour, he said, and the team is encouraged to meet that goal.

His record? "Seven hundred eighty-five," he said without blinking.

The robots are one of many ways Amazon has brought more efficiency and speed to its network. In the North Loop, Amazon has about 150 tech workers working on new transportation technology, delivery services and its fast-growing cloud-computing division.

Among the projects the group has worked on are Amazon lockers, which provide a way for customers to pick up their online orders in shopping malls, grocery stores and other retail locations.

The company said a few weeks ago that it will add an additional 200 jobs at the North Loop office, where it takes up almost half of the seven-story T3 building. That same week, Amazon also announced it would add thousands of jobs at tech hubs in Boston and Vancouver.

That's on top of the 45,000 jobs Amazon already has at its Seattle headquarters — and up to 50,000 more coming to the city that lands its second corporate campus.

In Shakopee, the fulfillment center is built around optimization at every step in the process. Items are randomly stored in pods based on which ones are emptiest, not by product category. The system tells packers which box best fits a product and spits out exactly the right amount of packing tape to fit that size box.

Russell said the robots have cut down on the amount of walking employees have to do and also created new opportunities for people in the company.

"This technology has allowed us to create some new jobs that didn't exist before," he said. "These roles are more skilled and require different levels of training."

Among those new roles, he said, are "amnesty floor monitors," whose job is to pick up products if they fall out of a pod. These workers use Kindles to create a virtual pathway to get to the items and block robotics traffic along the route.

Other retailers including Richfield-based Best Buy and Target are also testing ways to bring more automation and robotics into their distribution centers as they look to become faster and more efficient to better compete with Amazon.

Casey Carl, Target's former chief innovation officer, said he expects of lot of big retailers to invest in this area.

"Robotics plus humans — that's going to be the answer for at least the next several years," he said. "They're replacing and displacing certain jobs and routines, but they're also creating a lot of other ones."

While robotics plays a big role in Amazon's fulfillment center, at least four humans will still touch a package before it goes out the door, Russell said.

In addition to the picking stations, there are areas where employees stock the pods full of products coming in from vendors or other Amazon facilities. There are packing areas where workers place the items in boxes. And there are people who load the trucks.

Some trucks head to Amazon's sorting center a few miles away where packages are separated by ZIP code and then to the closest Postal Service office to help speed up deliveries. Same-day delivery orders head to the delivery station in Eagan from which packages are sent out in vans to customers' doorsteps.

Amazon's deliveries within an hour or two are handled from the Prime Now hub in Minneapolis where drivers, who work on an arrangement similar to Uber and Lyft, stream in and out throughout the day to pick up orders.

On the walls in many of Amazon's buildings, from the fulfillment center to the Prime Now hub, are the same words to encourage workers in large letters: "Work Hard. Have Fun. Make History."